I just briefly searched online here and on the net in general, and supposedly this type of gauge is least accurate but some people have still found them good enough. There was some mentioning of lubricating them (when they’re old) to get them to be more accurate again.
And one thread online mentions they tend to read under the real pressure:
but this got me a bit curious. Do pencil gauges in general read under or over when they’re off? And which case does lubricating actually help with? I would assume the reading under case as the lubrication would make it slide easier/faster so it would then be more accurate if off to begin with. Lubricating one that’s reading over could make it read even more over due to sliding out easier?
From my experience so far with the gauges I have around (pencil and one or two cheap dial gauges), when they’re really off the pencil ones seems to be over reading than under. Hence trusting them would lead to under inflation over time. I think that happened to me when I new even less about cars & car maintenance as a young adult.
In recent a recent check today, my current trustable pencil gauge is within range enough when checking my car as i told tire shop to put 35 psi on my tires and the gauge reads close enough to it at 36-37 in warm sunny weather. I used it to check another family car and it read tires being under inflated. I then took out gauges that were in that car (one pencil, one cheap dial) to check to see if it was incorrect based on using those gauges. That pencil one over read, and the dial under read (by 2-3 psi I think).